9 skin conditions that could signal a more serious problem

patient doctor skin

• Many internal health conditions can cause symptoms in the skin .
• INSIDER spoke with a dermatologist about some skin signs of internal illness.
• Conditions like lupus, inflammatory bowel disease, diabetes, and over- or underactive thyroid can affect the skin in distinctive ways.

The skin is your body's largest organ, so it's not too surprising that many internal illnesses can cause changes to the skin, too.

"In a way, you can think of your skin as a window into the internal body," Dr. Kathleen Suozzi , assistant professor of dermatology at Yale School of Medicine, told INSIDER. "The vast majority of different medical conditions can manifest with complications, reactions, or findings on the skin."

Compiling a list of every skin symptom of every internal illness would be difficult Suozzi characterized this as a "huge" topic to which "whole textbooks" are dedicated but there are some distinctive skin changes that may be early signs of serious systemic health conditions.

Read on to learn about some examples.

1. Itching

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"Sometimes if a patient has intractable itch, we'll check ...to make sure they don't have Hodgkin lymphoma," Suozzi said. "Rarely, that can be a presenting sign."

Hodgkin lymphoma is a type of cancer that affects white blood cells called lymphocytes, and the mostcommon symptom of the disease is an enlarged lymph node in the neck, the armpit or the groin, according to the American Cancer Society.

It's also important to remember that there are many, many other health conditions that aren't cancer that can also cause itchy skin .

2. Thicker, darker skin on some parts of the body

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Suozzi said that a condition called acanthosis nigricans (AN), in which the skin thickens and darkens in certain areas, can be a sign that someone has diabetes.

"It's an area of hyperpigmentation, or darkening of the skin, that occurs in the skin folds," she said. "Classically [it happens] in the back of the neck, or in the creases of the arms. Especially in kids, that's a sign that you might want to check them for diabetes."

The condition can also occur in completely healthy people or happen because of certain medications or other conditions , according to the American Academy of Dermatology (AAD).

3. Warm, sweaty skin or cold, dry skin

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An overactive or underactive thyroid can cause changes in how your skin feels, Suozzi explained.

The thyroid is a butterfly-shaped gland in the neck . It releases hormones that work to regulate metabolism, heart rate, body temperature, and more. But in some people, the thyroid can be overactive, making more thyroid hormones than the body requires (a.k.a. hyperthyroidism ), or underactive, making too little ( a.k.a. hypothyroidism ). Both conditions lead to a wide array of possible symptoms across the whole body, including the skin.

Read more : 17 things you need to know about your thyroid because it controls a lot more in your body than youd think

"In general, with overactive thyroid, your skin is warm and moist due to increased sweating, versus underactive thyroid, [when the skin] can be cold, pale, rough, and dry," Suozzi said.

4. Hair loss or thinning

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"Patients with thyroid disease can also get hair changes," Suozzi said. "So if a patient present with hair loss, we will sometimes, depending on the quality of the hair loss, check their thyroid function."

She said that people with an overactive thyroid can experience hair thinning, while people with an underactive thyroid can lose hair in a very specific place: The outer third of their eyebrows.

5. Darkening skin

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In Addison's disease , the adrenal glands which sit just on top of the kidneys don't produce enough of the hormones cortisol and aldosterone.

The most common symptom of Addison's disease is fatigue , according to the National Organization for Rare Disorders (NORD), but it can also cause skin changes.

Suozzi explained that hormonal changes in Addison's disease patients can make the skin more pigmented,

"These patients look tan," she said.

NORD adds that this darker, or hyperpigmented, skin can also occur in patches , often near scars or skin creases like knuckles. In fact, these skin changes can happen years before other symptoms of Addison's disease develop , according to NORD.

6. Sensitivity to sun

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Sun sensitivity is one of many different skin signs that could indicate lupus, a condition in which the body's immune system attacks its own organs and tissue.

In fact, Suozzi said, certain skin symptoms are part of the criteria doctors use to diagnose lupus.

"One thing would be photosensitivity reacting more than normal to sun exposure," she said. (About 50% of people with lupus experience this sensitivity , according to the Johns Hopkins Lupus Center.)

She added that certain rashes can also denote the disease. The first is a malar rash (also called a "butterfly rash," so named because it spreads across both cheeks in a butterfly shape. The second is called a discoid lupus rash , she said.

Finally, mouth ulcers can also be a skin sign of lupus the mucous membrane inside your mouth is considered part of your skin, Suozzi explained.

7. A hump between the shoulders

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In Cushing's syndrome , the adrenal glands produce an excess of the stress hormone cortisol. One of the condition's many symptoms is a fatty hump situated between the shoulders.

"We call it the buffalo hump," Suozzi said. "It's a roundness on the upper back below the neck."

"[Cushing's syndrome] patients can also get stretch marks called striae that sometimes just erupt," she added. "That can be a presenting sign of the disease."

8. A type of tender bump under the skin

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Suozzi said that inflammatory bowel disease (IBD), an umbrella term that includes Crohn's disease and ulcerative colitis, can manifest with specific skin symptoms.

"One is called pyoderma gangrenosum it's these eroded lesions that show up on the legs and they don't heal," she said. "And if young patients get that, we always look to make sure they don't have Crohn's disease or ulcerative colitis." (You can see a photo of pyoderma gangrenosum at the Mayo Clinic website , but be warned that it's graphic.)

Another possible skin sign of IBD is erythema nodosum, she added. This is when tender, red bumps form under the skin , often on the shins but sometimes elsewhere on the body.

"It can show up in patients for a variety of reasons, but it does make us go look [for IBD]," Suozzi said.

9. A type of rash on the backs of the hands

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Dermatomyositis is a condition that can cause both muscle weakness and distinctive skin issues.

"[It's a] less common autoimmune disorder, but it has very characteristic skin findings," Suozzi said.

One is a rash called Gottron's papules that appears on the back of the hands, Suozzi said.

Another is called the shawl sign . It's a red rash that covers the shoulders, arms, and upper back in a pattern that resembles a shawl.